Is there any research work on the usefulness of the concept of "personality" for an AGI?
'Personality' is something of a 'suitcase word' (Minsky) for quite a large collection of (presumably reasonably consistent) observable traits. 

It seems clear that there is a certain collective advantage in having a consistent personality - specifically that it affords observers some learning gradient in an otherwise uncertain environment. This is of particular importance because those consistencies might have been arrived at using different learning mechanisms than the ones a given observer has.

Hence, in any non-trivial coevolutionary system, other organisms will inevitably make use of any such consistencies. Consider a simple robot, called Alice, say, that has the trait of 'quickly flashing red when it sees a blue robot'. It makes sense for all observers to exploit everything that they perceive as correlating with Alice's behavior, in particular, the prediction that a blue robot is likely to be present.

The best reference I can recommend on this (which shows that we tend to ascribe 'personality' to even very simple mechanisms) is 'Vehicles' by Valentino Braitenberg.